Question about magnetic induction

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Discussion Overview

The discussion revolves around the concept of magnetic induction as it relates to a current-carrying wire moving in a uniform magnetic field. Participants explore the implications of this setup, including the forces acting on the wire and the induced electromotive force (emf) resulting from changes in magnetic flux.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes a scenario where a current-carrying wire experiences a force when placed in a magnetic field, suggesting that as it moves, it induces an emf that opposes the existing current.
  • Another participant questions how the number of magnetic field lines changes if the magnetic field is uniform and the wire is not rotating, prompting a discussion about the nature of magnetic flux.
  • A participant clarifies that while a back emf is induced in a moving conductor, this does not necessarily mean the current will be zero, especially in ideal conditions without energy losses.
  • There is a suggestion that if the area of the circuit increases, this could lead to an increase in the magnetic lines within the circuit, resulting in induced current.
  • One participant notes that in the presence of resistance, the relationship between back emf and supply emf is modified, indicating that back emf equals supply emf minus the product of current and resistance.

Areas of Agreement / Disagreement

Participants express differing views on the mechanics of magnetic induction in this scenario, particularly regarding the change in magnetic flux and the implications for current flow. No consensus is reached on these points.

Contextual Notes

Participants discuss the effects of ideal versus non-ideal conditions, including energy losses and resistance in the circuit, which may influence the behavior of the system but are not fully resolved in the discussion.

max11011
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hi everyone iam happy to join physics forums
i 'd like to ask a question about magnetic induction
if i have a current carrying wire(connected to a battery=V) of length (L)& of intensity (I) & perpendicular to a uniform magnetic field(B) then a force act on it (F=LIB)
so when it moves...if it changes the no. of magnetic field lines inside its circuit then it induces emf also a current which is oppostie to the one already passing in the circuit so the (F) decreases gradually until the induced emf become equal to the emf of the battery
so the final situation
Wire with no current (because of equilibrium that happened) moving with constant velocity...

is that right?...or i have missed something...
 
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welcome to pf!

hi max11011! welcome to pf! :smile:
max11011 said:
if i have a current carrying wire … perpendicular to a uniform magnetic field(B) then a force act on it (F=LIB)
so when it moves...if it changes the no. of magnetic field lines inside its circuit …

but why would it change the number of field lines (the magnetic flux)?

it's not rotating, and the field is uniform, so won't the lines cut ("cookie-cutter" style) stay the same? :confused:
 
Max: Yopu have picked up on 2 effects here
1) When a current carrying wire is placed in a magnetic field it experiences a force (BIL)
this is the principle behind the electric motor.
2) When a conductor moves through a magnetic field an emf is induced that opposes the change producing it. In an electric motor this is known as a 'back emf'
In an ideal case, with no energy losses, the motor will reach a speed where the back emf = the applied emf.
This does not mean the current will be zero ! If there are no energy losses it is possible to have a current with no resultant emf !
 
Thanks. ..tiny-tim for ur reply
but Although the field is uniform and no rotation...,the area of the circuit increases gradually so does the magnetic lines in the curcuit consequently...a current is indced.
The picture may make it more clear.

Thanks. ..truesearch...for ur reply...
so if the motor or the current carrying wire isn't ideal the back emf wouldn't equal forward emf.
 

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hi max11011! :wink:
max11011 said:
Thanks. ..tiny-tim for ur reply
but Although the field is uniform and no rotation...,the area of the circuit increases gradually so does the magnetic lines in the curcuit consequently...a current is indced.
The picture may make it more clear.

ah, yes, if the area is increasing :smile:

(btw, shouldn't "dots" be coming up towards us? :wink:)
 
If there is resistance in the circuit then the back emf will equal the supply emf -Ir.
This is the simplest case to consider when there is resistance present
 

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